Positron Emission Tomography (PET) captures gamma photons produced in a human body when a positron is annihilated, and obtains the distribution of a positron nuclide tracer inside the human body, to obtain pathophysiological characteristics such as organ functions and metabolism.
The accuracy of information carried by the gamma photons such as energy, position and time directly affect imaging performance of the system. A critical component of the PET system is the scintillation pulse acquisition and processing unit, whose main functions include processing a scintillation pulse formed by a front detector, to acquire information carried by the gamma photons such as energy, position and time. In order to ensure the performance of the PET system, it is desired that the employed scintillation pulse acquisition and processing unit has such features as high precision, stable performance, real-time correctability, and high integration level.
The Multi-Voltage Threshold (MVT) sampling method is an inexpensive and efficient solution to digitalize a scintillation pulse from a nuclear medicine apparatus such as PET. The method uses a plurality of voltage thresholds appropriately determined according to the characteristics of the scintillation pulse, and realizes digitization sampling of the scintillation pulse by digitizing the time at which the scintillation pulse crosses a voltage threshold. MVT digitization devices developed based on the method have been applied to PET systems, and most of the MVT digitization devices are composed of a comparator and a time-to-digital converter. Specifically, the comparator is for comparing the scintillation pulse with voltage thresholds and outputting a hopping signal when the scintillation pulse crosses a voltage threshold; the time-to-digital converter is for digitization sampling the time at which the hopping signal is output by the comparator.
In order to avoid a sampling error resulting from the difference between comparing voltage and actual voltage thresholds due to comparator precision, most existing MVT digitization devices include a high-precision comparator. Using such a high-precision comparator can solve the above issue to a certain extent, but drastically increases the cost of the digitization device as a whole. Moreover, such a high-precision comparator imposes a high requirement on the working environment, and its power consumption is high; hence the cost of the whole MVT digitization device is too expensive and the channel density is low.
Therefore, in view of the problem in the prior art, it is desired to provide a new method for correcting a threshold of a multi-voltage threshold sampling digitization device, to lower the requirement on comparator precision in implementation of the MVT digitization device.